1. Field of the Invention
The present invention generally relates to a recording and reproducing device and a recording and reproducing head used therein, more particularly to a recording and reproducing device in which a positioning error of a recording and reproducing head due to vibration and impact is detected accurately and the recording and reproducing head used therein.
2. Description of the Prior Art
Currently, along with a high integration and a miniaturization of a magnetic disc as a recording and reproducing device, a magnetic head assembly having a magnetic head which records and reproduces data has been miniaturized. Because of the miniaturization, the device is very susceptible to vibration or impact. An off-tracking, wherein a magnetic head for recording or reproducing is moved off a track in which data is recorded, occurs easily due to the vibration and impact. Therefore, an off-tracking correction is indispensable in the magnetic head assembly. However, the off-tracking does not always occur when the vibration occurs. Therefore, an accurate detection of the off-tracking is desired.
In the magnetic disc device, magnetic heads are arranged facing one or both surfaces of the magnetic disc. The magnetic head is mounted at one end of a suspension which is fixed at one end of a carriage arm of an actuator. By driving the actuator, the magnetic head moves in a radial direction of the magnetic disc.
FIGS. 1A and 1B are schematic illustrations showing a magnetic head assembly of a conventional magnetic disc device. In FIG. 1A, the magnetic head assembly has a suspension which is a metal plate such as stainless steel bent at a certain angle. At a front end of the suspension 12, a magnetic head 13, in which a thin-layer head is provided on a slider, is mounted through an adhesive. At a back end of the suspension 12, a fixing hole 14 is formed. In this case, the magnetic head 13 is a composite thin-layer magnetic head comprising a thin-layer magnetic head for recording and a magnetoresistance effect (MR) head for reproduction.
In the suspension 12, a signal pattern 15 for transmitting four signals for recording and reproduction to the magnetic head 13 is formed. A front end thereof is connected to terminals of the magnetic head 13 and a back end thereof is formed as lead terminals 16 provided on a side of the suspension 12.
In the signal pattern 15, as shown in FIG. 1B, an insulating layer 17 is formed on the baseboard 12a of the suspension. On the insulating layer 17, four signal patterns 15 are made, for example, by etching copper. On the signal patterns 15, an insulating protective layer 18 having a thickness of several microns is formed. At the back end of the suspension 12 except where the fixing hole 14 and the signal pattern 15 are formed, a dummy pattern 19 of metal is formed in order to maintain an equal thickness of the protective layer 18. That is, the protective layer 18 is formed on the whole surface of the signal pattern 15. The magnetic head suspension assembly 11 is fixed on the actuator.
FIG. 2 is a plan view showing the actuator.
In FIG. 2, the actuator 20 comprises a plurality of carriage arms 22 rotated about a rotation axis 21 and a voice coil motor (VCM) 23 having a voice coil (not shown) as a driving means. In the front end portion 22a of carriage arm 22 in which an installation hole 24 is formed, the above-mentioned magnetic head assembly 11 is provided.
FIGS. 3A and 3B are schematic illustrations showing the conventional composite thin-layer magnetic head in which FIG. 3A is a partial perspective view and FIG. 3B is a sectional view. FIG. 4 is a partial perspective view showing a conventional magnetic head slider.
FIGS. 3A and 3B show the composite thin-layer magnetic head 13 in which an electromagnetic conversion head (recording head) and magnetoresistance effect (MR) head (reproducing head) are combined. In FIGS. 3A and 3B, the magnetoresistance effect head (MR head) comprises a non-magnetic baseboard 32, a magnetoresistance effect element (MR element) 33 of a rectangular shape formed on the non-magnetic baseboard 32, conductive lead layers 34a (34b) provided at both ends of the MR element 33, an upper magnetic shield layer 35a and a lower magnetic shield layer 35b.
The conductive lead layers 34a, 34b are cut off at a certain width in the longitudinal direction of the MR element 33 and are connected to both ends of an MR layer of the MR element 33. The MR element 33 and the conductive lead layers 34a, 34b are formed between the upper magnetic shield layer 35a and the lower magnetic shield layer 35b and are electrically insulated by non-magnetic insulating layers 36.
In the electromagnetic conversion head (inductive head) 37 for recording data onto the magnetic disc 30, a recording gap 38 including alumina (Al.sub.2 O.sub.3) is formed on the upper magnetic shield layer 35a of the MR head 31 also serving as a lower magnetic pole (first magnetic pole). On the recording gap 38, an inner insulating layer 39, a conductive thin-layer coil (Cu) 40 and an upper magnetic pole 41 are formed sequentially. A horizontal recording of the data is conducted by the recording gap 38 formed between the upper magnetic pole (second magnetic electrode) 41 and the lower magnetic pole (upper magnetic shield layer) 35a. A protective insulating layer 42 is formed on the upper magnetic pole 41.
In the magnetic head slider 42, as shown in FIG. 4, two rail faces 42a, 42b are formed on the magnetic disc 30. Each head element is provided on a backside of one of rail faces 42a.
FIGS. 5A and 5B are schematic illustrations showing the magnetic disc 30. In FIGS. 5A and 5B, plural data portions 43 are formed on concentric circles of the magnetic disc 30. Between the data portions 43, track gaps 44 which are not used for storing user data are formed. A prescribed number of servo frames 45 are provided in a radius direction at a certain angle. The user's data is recorded in the data portions 43 of each track 43.sub.1, 43.sub.2.
In the magnetic disc device of the data surface servo type shown in FIGS. 5A and 5B, since the servo data is recorded in servo frames 45 between the data portions 43, no controls are available between the servo datum.
Therefore, the servo signal cannot be read to position the magnetic head 13 on-track during a read or write operation and the off-tracking correction is difficult to do.
That is, when the off-tracking occurs during the read operation, the data is misread or a read error occurs. When the off-tracking occurs during the write operation, the data recorded on the adjacent track may possibly be destroyed and cannot be recovered especially in a high-density magnetic disc.
Japanese Laid-Open Patent Application No. 1-229454 discloses a plurality of disturbance detectors provided in a frame, a base, a carriage (actuator 20), a magnetic head and so on in order to detect a disturbance to stop the read/write operations.
FIG. 6 is a circuit diagram showing a method for detecting the off-tracking. In FIG. 6, a detected signal from an impact sensor 52 as a disturbance sensor is input to a comparator 51 through an amplifier 53. In the comparator 51, the signal is compared with a determined level from a level slice circuit 54. When the disturbance is detected, the signal is input to a latch circuit 55. An output signal of the latch circuit 55 is transmitted to a digital signal processor (DSP) 56 and a read/write controller 57. The read/write controller 57 makes a write gate signal become an off state to stop supplying data to the head 13 during a write operation. Also, the read/write controller 57 makes a read gate signal become off state to stop a read operation during the read operation. In FIG. 6, the signal from the read/write controller is amplified by an amplifier 58.
FIGS. 7A and 7B are a schematic illustrations showing the off-tracking in the conventional magnetic head. In FIG. 7A, when the disturbance and the vibration are not detected by the impact sensor 52, the MR head 31 and the inductive head (electromagnetic conversion head) 37 are on a prescribed track 43 (43.sub.2).
When the magnetic head 13 is off the track, a positioning error by which the MR head 31 and the inductive head 37 cross over the track gaps 44 adjacent to the track 43 (43.sub.2) leads to the read error, as shown in FIG. 7B. When the impact sensor detects the disturbance, the read operation stops and a tracking operation is conducted so as to reposition the magnetic head on the track.
The Japanese Laid-Open Patent Application No. 5-101520 discloses a method for detecting a disturbance in which the disturbance is detected by a magnetic head which does not perform a read/write operation.
However, in the method disclosed in Japanese Laid-Open Patent Application No. 1-229454, only a certain level of the impact can be detected by the impact sensor 52. Also, even when head core center (core of the MR head 31 and inductive head 37) is on the center of a track, that is, a relative position therebetween is not changed, the disturbance may be detected and the read/write operation stops, which deteriorates the performance of the device.
Besides the impact, when the center of the head core does not correspond to that of the track due to a disturbance of a VMC control current, the disturbance cannot be detected and read/write operation is continuously conducted. In this case, the data recorded on the track is destroyed or misread.
In the method disclosed in the Japanese Laid-Open Patent Application No. 5-101520, the off-tracking is detected by another magnetic head continuously reading the signal during read/write operation.
However, there may be a situation in which the magnetic head which performs read/write operation is off the track and the another magnetic head is on the track, due to a specific vibration. In this case, the read/write operation is continued.
On the contrary, when the magnetic head which performs the read/write operation is on the track and the magnetic head detecting the off-tracking is off the track, the read/write operation stops.
The present invention is developed in order to solve the problems described above.